feat: add first-party skills, ponytail lock, and full lint suite

- add ponytail skill set to skills-lock.json (14 locked skills total)
- add first-party medusa skill under skills/, layered on install
- make test now runs ruff, shellcheck, and markdownlint-cli2
- CI installs the lint tools before make test in both workflows
- MIT license, funding buttons, thanks and donation sections in README
- .markdownlint-cli2.jsonc config; ignore lint caches in .gitignore

Makefile

@@ -9,10 +9,12 @@ project:
 	@test -n "$(TARGET)" || { echo "usage: make project TARGET=/path/to/repo"; exit 2; }
 	@TARGET="$(TARGET)" bash scripts/install.sh
 
-# Validate skills-lock.json and shellcheck the scripts.
+# Validate the lock, lint Python (ruff), scripts (shellcheck), and markdown.
 test:
 	@python3 -m unittest discover -s tests -v
+	@if command -v ruff >/dev/null; then ruff check .; else echo "ruff not installed - skipped"; fi
 	@if command -v shellcheck >/dev/null; then shellcheck scripts/*.sh; else echo "shellcheck not installed - skipped"; fi
+	@if command -v markdownlint-cli2 >/dev/null; then markdownlint-cli2 "**/*.md"; else echo "markdownlint-cli2 not installed - skipped"; fi
 
 # Update all skills to their latest versions and refresh skills-lock.json.
 update: